linux-kernel - Re: utrace, RCU and ia64

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Date:	Tue, 17 Apr 2007 15:20:48 +0400
From:	Alexey Dobriyan <adobriyan@...ru>
To:	Roland McGrath <roland@...hat.com>
Cc:	akpm@...l.org, linux-kernel@...r.kernel.org, devel@...nvz.org
Subject: Re: utrace, RCU and ia64

[double freeing of struct utrace leading to oops in
 __rcu_process_callbacks]

Hi, Roland,

utrace debugging you've put into 2.6.21-rc6-mm1 helped. Two double-frees
reproduced:
1) BUG at kernel/utrace.c:176
	rcu_utrace_free
	utrace_reap
	utrace_release_task
	release_task
	flush_old_exec
	load_elf_binary
	search_binary_handler
	do_execve

2)	rcu_utrace_free
	check_dead_utrace
	remove_detached
	finish_report_death
	utrace_report_death
	do_exit
	debug_mutex_init
	get_signal_to_deliver
	do_notify_resume
	ptregscall_common
	sysret_signal
----------------
I've sprinkled more atomic_set's over utrace code to determine who is at
fault of first freeing. It seems to be

	rcu_utrace_free
	check_dead_utrace
	wake_quiscent
	utrace_detach

It was atomic_set(&utrace->debug, 42) right before wake_quiscent() call
and printk() in rcu_utrace_free() call. So it was 42 or garbage.

How I understand all this is that check_dead_utrace() can free struct
utrace, and don't clear ->utrace pointer.

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/